Coated articles such as transparent shower doors and IG window units are often heat treated (HT), such as being thermally tempered, for safety and/or strengthening purposes. For example, coated glass substrates for use in shower door and/or window units are often heat treated at a high temperature(s) (e.g., at least about 580 degrees C., more typically from about 600-650 degrees C.) for purposes of tempering.
Diamond-like carbon (DLC) is sometimes known for its scratch resistant properties. For example, different types of DLC are discussed in the following U.S. Pat. Nos. 6,303,226; 6,303,225; 6,261,693; 6,338,901; 6,312,808; 6,280,834; 6,284,377; 6,335,086; 5,858,477; 5,635,245; 5,888,593; 5,135,808; 5,900,342; and 5,470,661, all of which are hereby incorporated herein by reference.
It would sometimes be desirable to provide a window unit or other glass article with a protective coating including DLC in order to protect it from scratches and the like. Unfortunately, DLC tends to oxidize and burn off at temperatures of from approximately 380 to 400 degrees C., as the heat treatment is typically conducted in an atmosphere including oxygen. Thus, it will be appreciated that DLC as a protective overcoat cannot withstand heat treatments (HT) at the extremely high temperatures described above which are often required in the manufacture of vehicle windows, IG window units, glass table tops, and/or the like.
Accordingly, those skilled in the art will appreciate that a need in the art exists for a method of providing heat treated (HT) coated articles with a protective coating (one or more layers) comprising DLC. A need for corresponding coated articles, both heat treated and pre-HT, also exists.
In this respect, U.S. patent application Ser. No. 11/798,920 (hereby incorporated herein by reference) discloses a method of making a coated article including a step of heat treating a glass substrate coated with at least a layer comprising diamond-like carbon (DLC) and an overlying protective film of zinc oxide thereon. In certain example embodiments, the protective film may be of or include both (a) an oxygen blocking or barrier layer, and (b) a release layer. Following and/or during heat treatment (e.g., thermal tempering, or the like) the zinc oxide based protective film may be entirely or partially removed.
Unfortunately, the pre-HT shelf life and/or stability of the coated articles of Ser. No. 11/798,920 are limited. For example, it has been found that the zinc oxide based protective film is susceptible to corrosion prior to heat treatment (after heat treatment, the protective film is often gone). Samples stored in moderately humid environments start to tarnish (when viewed from the glass side) suggesting that over time moisture is penetrating the zinc oxide based protective film and reaching the DLC. Also, films of Ser. No. 11/798,920 as deposited are unable to pass the one hour in condensing high heat and high humidity (50 C./95 rH) testing environment.
Accordingly, it will be appreciated that there exists a need in the art to improve the shelf-life and/or stability of coated articles such as those of Ser. No. 11/798,920 so that they are less likely to tarnish prior to heat treatment (HT).